package com.langyastudio.edu.common.util;

/**
 * 描述: Twitter的分布式自增ID雪花算法snowflake (Java版)
 * <p>
 * https://segmentfault.com/a/1190000039087285
 * https://github.com/souyunku/SnowFlake
 **/
public class SnowFlakeT
{
    /**
     * 起始的时间戳
     */
    private final static long START_STMP = 1611813893709L;

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT   = 12; //序列号占用的位数
    private final static long MACHINE_BIT    = 5;   //机器标识占用的位数
    private final static long DATACENTER_BIT = 5;//数据中心占用的位数

    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATACENTER_NUM = ~(-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM    = ~(-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE       = ~(-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long MACHINE_LEFT    = SEQUENCE_BIT;
    private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long TIMESTMP_LEFT   = DATACENTER_LEFT + DATACENTER_BIT;

    private final long datacenterId;  //数据中心
    private final long machineId;     //机器标识
    private       long sequence = 0L; //序列号
    private       long lastStmp = -1L;//上一次时间戳

    /**
     * SnowFlake
     *
     * @param datacenterId 数据中心
     * @param machineId    机器标识
     */
    public SnowFlakeT(long datacenterId, long machineId)
    {

        if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0)
        {

            throw new IllegalArgumentException("datacenterId不能大于MAX_DATACENTER_NUM或小于0");
        }
        if (machineId > MAX_MACHINE_NUM || machineId < 0)
        {

            throw new IllegalArgumentException("machineId不能大于MAX_MACHINE_NUM或小于0");
        }
        this.datacenterId = datacenterId;
        this.machineId = machineId;
    }

    /**
     * 产生下一个ID
     *
     * @return long
     */
    public synchronized long nextId()
    {
        long currStmp = getNewstmp();
        if (currStmp < lastStmp)
        {

            throw new RuntimeException("时钟向后移动。拒绝生成ID");
        }

        if (currStmp == lastStmp)
        {

            //相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;
            //同一毫秒的序列数已经达到最大
            if (sequence == 0L)
            {

                currStmp = getNextMill();
            }
        }
        else
        {
            //不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastStmp = currStmp;

        return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                | datacenterId << DATACENTER_LEFT       //数据中心部分
                | machineId << MACHINE_LEFT             //机器标识部分
                | sequence;                             //序列号部分
    }

    private long getNextMill()
    {
        long mill = getNewstmp();
        while (mill <= lastStmp)
        {

            mill = getNewstmp();
        }

        return mill;
    }

    private long getNewstmp()
    {
        return System.currentTimeMillis();
    }
}